As a method of identifying whether or not a desired object exists in a certain space, the following method exists.
For example, the technology of imaging the image of the space in which no marker exists as a background video image with an video image inputting means in a marker generation stage, extracting feature points from the above background video image, mapping these feature points onto an invariant feature space, thereby to define them as invariant features, defining portions in which these invariant features do not appear as unique features, generating a marker pattern based upon these unique features, and in a marker detection stage, imaging the image of the space containing the object added with the marker as a detection-targeted video image, extracting the feature points from this detection-targeted video image, determining whether or not a segment matching with an arrangement of the feature points extracted from the marker pattern exists in an arrangement of these feature points, and detecting this as the marker when the matching one exists (for example, see Patent Literature 1).
With this technology, the pattern not appearing in the background video image can be generated as the marker pattern in the marker generation stage. This prevents the marker from being erroneously detected from a location in which no marker exists, out of the detection-targeted video images, thereby enabling the marker added to the objet to be surely detected in the marker detection stage.